1. Field of the Invention
The present invention relates to a bi-directional damper valve for dampening oscillation in a hydraulic system, to a power steering system incorporating the damper valve, and to methods of using the valve. More particularly, the present invention relates to a bi-directional damper valve which includes a main valve body having a hollow passage formed therethrough, and a pair of opposed spring-loaded poppets disposed in a central chamber of the valve body, as well as to a system incorporating the insert, and to methods of using the insert.
2. Description of the Background Art
Power steering is in common use on many cars and trucks sold today.
During operation of a vehicle, a driver can experience some unpleasant feedback sensations at the steering wheel, due to unusual conditions. Examples of some of these unpleasant feedback situations include steering shimmy, brake judder, and tire kickback.
Unwanted steering vibration feedback diminishes driving enjoyment and, hence, affects vehicle marketability. Auto manufacturers have been struggling with this phenomenon for some time, and are constantly looking for ways to improve power steering feel.
A number of different restriction valves are known for use in hydraulic power steering systems. Some of the known restriction valves are designed to try and reduce the unpleasant feedback sensations referred to above.
Some steering system suppliers have designed fluid dampers to place in the steering system, in order to reduce steering vibrations. These known dampers are designed to provide a flow restriction in the lines connecting the gearbox control valve to the gearbox cylinders, in order to resist mechanical movement disturbance of the rack.
Some examples of issued patents relating generally to the fields of power steering stabilizers, hydraulic flow control valves, and related hardware include U.S. Pat. Nos. 3,894,562, 4,285,534, 4,736,962, 5,531,287, 5,697,216, and 6,119,728.
The hydraulic dampers currently used by most automotive companies, in power steering systems for passenger cars and trucks, are similar to each other in design and function. The currently known damper generally consists of a one-way valve and a damping valve with a threshold pressure, and an inlet restrictor to tune the dampening effect. These valves are usually integrated in parallel in a damper housing, to receive flow in opposite directions. Fluid flow in one direction travels through the one-way valve, while fluid flow in the other direction flows through the inlet restrictor.
In the current damper, when the steering wheel is turned, the one-way valve allows the fluid to flow from the power steering high-pressure line into the gearbox cylinders. The damping valve has a threshold pressure to resist return flow from the steering cylinder to the gearbox control valve. By functioning in this way, the known damper adds certain degree of rigidity to the fluid in the cylinder and the rack, when the tie rod receives external mechanical disturbance. Nevertheless, this threshold pressure inevitably adds an extra resistance to normal steering maneuvers, and hence, contributes a drag or friction feeling to normal steering wheel handling.
Although they do have a positive effect in reducing steering vibrations, the current power steering dampers detract from the feeling of normal steering maneuvers, by generating increased resistance to turning, and poor returnability. These negative effects are caused because the characteristics of the current power steering dampers are substantially independent of frequency.
Although the known power steering dampers have some utility for their intended purposes, a need still exists in the art for an improved power steering damper valve, and for a power steering system incorporating such a damper valve. In particular, there is a need for a hydraulic damper valve which will improve normal steering feel, while still providing a beneficial damping effect when needed.